A cancer research scientist who was tortured by a moral dilemma over animal experimentation waged a sabotage campaign against companies linked to the animal testing firm Huntingdon Life Sciences. Joseph Harris, 26, a doctor of molecular biology at Nottingham University, was jailed for three years yesterday after he became the first person to be convicted under legislation aimed at animal rights activists.

The scientist turned saboteur after claiming he had come under increasing pressure to carry out animal research to further his career, Northampton crown court heard. He believed that animal experiments caused unjustified suffering.

Harris, a published author of medical research into gastro-intestinal cancer, also said he split up with a girlfriend who could not accept his work and the fact that he might have to do animal research, the court was told.

He attacked three companies which had contracts with Huntingdon Life Sciences. The scientist, from Bursledon, Hampshire, pleaded guilty last month to three counts of interfering with a contractual relationship so as to hurt an animal research organisation, under the Serious and Organised Crime Act.

In December 2005 and January this year he broke into three companies in Nottingham, Bicester and Northampton, causing more than £25,000 of damage.

The court heard that although he had no affiliation to the animal rights group, he found the firms' details through the Stop Huntingdon Animal Cruelty website. He glued locks, slashed tyres and put hoses through letter boxes, flooding offices. One of the companies was a Northampton-based builders' merchant, supplying machinery to help the construction of a wing at the laboratory. All three companies have since stopped trading with HLS.

Harris was arrested at the scene of his third attack on January 15, at the builders' merchants, and DNA tests and chemical analysis of spray paint cans found on him linked him to the earlier crimes.

He carried out his first attack on December 16 last year - the same day he was awarded his PhD - attacking the Nottingham base of York Refrigeration, which maintained fridge equipment for HLS.

Harris had broken into the yard and daubed graffiti on the company's vans and walls, including the initials "ALF" and "now you will pay for your crimes".

The scientist was working at the University of Nottingham's academic unit of cancer studies, on a treatment for pancreatic cancer. He has since been dismissed, the court was told.

Rebecca Trowler, defending, told the court Harris was unhappy that animal experiments were used in cancer research.

"He has a genuine concern for the world - in particular his belief that the experimentation on animals which causes suffering is never justified - notwithstanding the progress it can produce for the human race."

Jailing him, Judge Ian Alexander said: "I am fully aware that your conviction and possibly the sentence I impose will seriously damage what was a very promising career. It may well be that your future inability to continue your research into gastro-intestinal cancer will be a great loss to those who suffer that disease."